This invention relates to microfluidic cartridges for analysis of liquid samples, and in particular to cartridges having a convoluted sample storage channel and to cartridges having a flow cytometric measuring region.
With the advent of micro-machining technology, microfluidic devices have proliferated (for example, U.S. Pat. No. 5,637,469 to Wilding et al., U.S. Pat. No. 4,983,038 to Ohki et al., U.S. Pat. No. 4,963,498 to Hillman et al., U.S. Pat. No. 5,250,263 to Manz et al., U.S. Pat. No. 5,376,252 to Ekstrom et al., E.P. Patent Publication 0381501B1, and Petersen, E. (1982) Proc. of the IEEE, vol. 70, No. 5, pp. 420-457). A practical limitation for particle-containing liquids such as blood is the sedimentation of particles within the device. Following loading the liquid in the device, appreciable particle sedimentation can occur within the time required to position the device in a measurement apparatus. For example, if the sample flow is slowed or stopped, blood cells can measurably settle out of plasma within 20 seconds. Without a sample management method and apparatus for sedimentation mitigation, quantitative analysis, especially using more than one analysis method sequentially, is impractical. Moreover, if samples are first collected and then transported to a measurement apparatus, as in a clinical setting or in field sampling, particle sedimentation can make accurate analysis impossible.
Microfluidic devices having sample storage reservoirs are known in the art (for example, E.P. Patent Publication 0381501B1). Because of particle sedimentation, these devices are useful only for samples without particles. Flow cytometric microfluidic devices are also known in the art (for example, U.S. Pat. No. 4,983,038 to Ohki et al.). Flow cytometric measurements are specifically applicable to particle-containing liquids. However, without sedimentation mitigation the measurements can be performed only immediately following sample collection.
The present invention provides an apparatus and method for storing a particle-containing liquid. The storage apparatus comprises a fluidic convoluted flow channel having a plurality of particle capture regions therein. Particle capture regions are bends in the channel that provide local gravitational minima. When sample flow is arrested (i.e. stopped or slowed) during operation or storage, each of the particles sediments in the nearest particle capture region. Unlike a storage reservoir, the particles do not aggregate in a single clump. Because the particles are locally captured in a plurality of regions, it is possible to rapidly and effectively reconstitute the sample following sedimentation. The storage channel is preferably spatially periodic, where the term spatially periodic channel is used herein for a channel having a substantially constant number of particle capture regions per unit volume. Spatial periodicity facilitates sample reconstitution. The storage channel is more preferably an isotropic spatially periodic channel, where the term isotropic is used herein for a channel suitable for storing a particle-containing liquid regardless of channel orientation.
The particles can be resuspended by either a continuous or a reversing flow. For resuspension by continuous flow, the arrested sample flow is re-started and particles rejoin the sample fluid. The leading edge and trailing edge of the sample storage segments are discarded, but the middle segment is resuspended to a homogeneous mixture identical to the original sample. For the suspension by a reversing flow, a plurality of resuspension cycles are employed. Each resuspension cycle includes a dispense portion to sweep a volume of the stored sample, and an aspirate portion to sweep the volume in the opposite direction. Flow rates, swept volume and number of cycle are tailored to the sample fluid.
This invention further provides a fluidic analysis cartridge having a convoluted storage channel therein. The cartridge contains a sample inlet, a convoluted sample storage channel in fluidic connection with the inlet, an analysis channel, having an analysis region, in fluidic connection with the storage channel, and a valve interface positioned between the storage channel and the analysis region. The inlet includes an inlet shut-off interface to prevent leakage ofthe stored sample through the inlet. The cartridge further includes a resuspension pump interface to resuspend a sedimented sample by sweeping the sample from the storage channel in a continuous or reversing flow. The convoluted storage channel enables accurate analysis of particle-containing samples. The sample analysis region provides for detection by any means known in the art, for example optical, electrical, pressure sensitive, or flow sensitive detection. For electrical detection, the cartridge can include an electrical interconnect. For optical detection, the cartridge can include a window positioned over the analysis region. The optical analysis can employ optical absorption, fluorescence, luminescence or scattering. Particularly useful are absorption and flow cytometric analyses.
A plurality of analysis channels can be included in a single cartridge. The analysis channels can be joined to reagent inlets to mix the sample with reagents such as diluents, indicators and lysing agents. The reagents can be fed into the cartridge using a pump, for example a syringe pump. The reagent can alternatively be stored in a reservoir in the cartridge. For microscale channels, having laminar flow, mixing ofthe reagent with the sample is predominantly diffusional mixing. A mixing channel can be positioned between the reagent inlet and the analysis region to allow mixing and reaction of the reagent with the sample. The cartridge can include additional valves and pumps for flow management. The analysis cartridge can be a self-contained disposable cartridge having an integral waste storage container to seal biological and chemical waste. The storage container can include a vent to release gases during fluid loading. The cartridge can have alignment markings thereon to facilitate positioning in an analysis instrument.
This invention further provides a disposable fluidic hematology cartridge and a method for using the cartridge. The hematology cartridge has both an absorption measuring channel and a flow cytometric measuring channel. The cartridge can include a convoluted storage channel. It can further include reagent inlets, mixing channels, a waste storage container, and valves and pumps. The flow cytometric measuring channel preferably has a means for forcing particles in the sample fluid into single file. This can be accomplished with a constricted flow passage. It is preferably accomplished using a sheath flow assembly.
This invention further provides a sheath flow assembly. The sheath flow assembly includes a sample channel and first and second sheath fluid channels positioned on either side of and converging with the sample channel. The assembly also includes upper and lower sheath fluid chambers positioned above and below and converging with the sample channel. The sheath fluid channels provide hydrodynamic focusing in the widthwise direction, and the sheath fluid chambers provide hydrodynamic focusing in the depthwise direction. Because the assembly provides hydrodynamic focusing, geometric focusing is not required. It is not necessary for the sample channel to contract in either the widthwise or depthwise direction. Contracting channels can also be employed.
A sample analysis instrument for use with a fluidic analysis cartridge is further provided. The instrument includes a cartridge holder, a flow cytometric measuring apparatus positioned for optical coupling with a flow cytometric measuring region on the cartridge, and a second measuring apparatus positioned to be coupled with a second analysis region on the cartridge. The cartridge holder can include alignment markings to mate with cartridge alignment markings. It can also include pump mechanisms to couple with pump interfaces on the cartridge and valve mechanisms to couple with valve interfaces on the cartridge.
The convoluted storage channel provides one means for resuspending particles sedimented during sample storage. This invention also provides analysis cartridges having a storage reservoir and an alternative resuspension means. The resuspension means can be an ultrasonic vibrator acoustically coupled to the reservoir or a mechanical agitator either positioned within the reservoir or mechanically coupled to the reservoir.
The flow cartridges of this invention can be formed by any of the techniques known in the art, including molding, machining and etching. They can be made of materials such as metal, silicon, plastics and polymers. They can be formed from a single sheet, from two sheets, or, in a preferred embodiment, from a plurality of laminated sheets. This invention further provides a method of fabricating a laminated fluidic flow channel. In the method, flow elements are formed in rigid sheets and abutting surfaces of the sheets are bonded together. The term rigid sheet is used herein for a substantially inelastic sheet. A rigid material still exhibits flexibility when produced in thin sheets. The flow elements can include fluid channels within the plane of the sheet, vias (holes) to route the fluid to the next layer, analysis regions, pump interfaces and valve interfaces. The flow elements can be formed by methods including machining, such as die cutting or laser ablating, and molding. The sheets can be bonded together by the use of an adhesive or by welding. They can alternatively be held together with mechanical compression.